Method of sealing charged bulbs



Jim 1941- A. J. LOEPSINGER 2,227,757

METHOD OF SEALING CHARGED BULBS FiledJuly 31. 1956 Alfie/Z Jiagvsa'zqger:

6. B Cittorneg Patented Jan. 7, 1941 UNITED STATES METHOD OF SEALING CHARGED BULBS Albert J. Loepsinger, Providence, R. 1., asslgnor to General Fire Extinguisher Company, Providence, R. L, a corporation of Delaware Application July 31, 1936, Serial No. 93,558

6- Claims.

This invention relates to an improved method of sealing charged bulbs. It is particularly applicable to scaling a bulb having an open tubulated portion with its end to be sealed in close proximity to a charge which has a higher coeilicient of expansion than the bulb itself. But the invention may also be employed with other forms of bulbs similarly charged. As an illustrative example orhow the improved method may be 10 practiced, I will describe its application to the sealing of a glass bulb charged with a highly expansible fluid.

, In the sealing of glass bulbs containing such a charge, the heat which must be applied to ef-.

feet the fusion of the glass has heretofore caused the contents of the bulb to expand more or less while the sealing is being effected. In some instances this is not of great moment, as for example, in the case of the ordinary thermometer tube where the end to be sealed is relatively remote from the end containing the mercury or other expansible liquid. In the sealing of such tubes, it is customary to keep the bulb ends in a cooling bath to prevent expansion of the expansible liquid itself, the cold medium of this bath serving also to absorb the heat conducted by the tube from the end which is being sealed.

Even in such cases, however, the vapor or air in the extended tube near its open end is necessarily heated and to some extent expands while the sealing is taking place. Where the bulb has a relatively short tubulated portion and the expansible charge is in close proximity to the end to be sealed. the expansion of the bulb's contents, while the sealing takes place, is of considerable importance. This expansion not only makes it diflicult to obtain a high percentage of well-sealed ends, but even where the seal is complete a portion of the material may be left thinner than what may be called the ordinary thickness of the bulb wall. It is manifest that such thin portions may lead to premature fracture and destruction of the bulb.

It is among the objects of the improved method to produce uniformly sealed bulbs having what is termed a deep seal. That is, it is intended that the fused material will be drawn together in a homogeneous mass so that the sealed end may be as strong, if not actually stronger, than the ordinary wall of the bulb. To this end it is an object-.of the invention to provide a method of sealing 'which comprises the initial closure of the tubulated end, prior to the actual sealing,

and further comprises the reduction of pressure within the closed bulb while the actual sealing occurs. This reduction of pressure within the then closed bulb tends to form a vacuum and as this occurs, the material of the tubulated portion is drawn together in a homogeneous mass which extends well along the said portion from its end 5 toward the body of the bulb. Thus the tubulated end is deeply sealed, and is uniformly strong, usually stronger than the wall of the bulb.

The accompanying drawing illustrates how my improved method may be practiced. For pur pose of illustration, I have chosen to show a bulb having a comparatively short tubulated end to be sealed, butit is to be understood that the practice of my invention is not limited to this particular form of bulb but may be used to ad- 15 vantage with other shapes and types of bulbs containing a charge which would ordinarily tend to expand while the sealing of the bulb occurs.

In the drawing:

Figure 1 is an elevation in section showing somewhat diagrammatically means for practicing the improved method;

Figure 2 is a similar view showing the initial closure of the tubulated end;

Figure 3 is another similar view showing the conditions as the sealing occurs;

Figure 4 is still another view showing the sealing completed; and

Figure 5 is a view of the finished bulb.

Referring more particularly to the drawing, the bulb I shown for purposes of illustration is made from glass and contains an expansible charge capable when the sealed bulb is heated to a predetermined temperature of completely shattering the bulb. Such bulbs are now used 35 as the heat responsive element of automatic sprinklers, frangible links and other devices where a highly dependable element is. expected to give way at some predetermined temperature. The bulb is initially made as seen in Figure 1 with 40 a closed end la and an open tubulated end lb.

A suitable expansible charge 2 is introduced through the open end until the bulb is nearly filled, for example to some point represented by the meniscus 2a. 45

The bulb is now ready for sealing and this must be accomplished at a fusion temperature much higher than that at which the liquid will rapidly expand. To avoid suchexp'anslon the nearly filled bulb is placed in a heat absorbing medium 5 except for its outstanding short tubulated neck lb. As illustrated, the bulb is placed upright on suitable supports 3 secured to the bottom of a container 4. This is so proportioned that when the container is filled with a heat absorbing liquid 5, the body of the bulb and the liquid therein are entirely below the surface of the cooling liquid and only the tubulated end projects above it. The cooling liquid is fed to the container by a tube 6 from a suitable supply under control of the valve 1. Around the container is a trough 8 into which the cooling liquid may overflow from the container and from which it may pass to waste through a drain 9.

To effect the sealing of the bulb, the tubulated end lb must be heated to the fusion temperature of the material. In the arrangement shown in the drawing heat is supplied by a bar i0 conheated by wires H and I2 to a controlled source of electrical energy. Either this bar is movable toward the bulb, or the container and bulb are movable toward the bar.

The steps of the improved method will now be described.

Let it be assumed that the heat absorbing medium 5, the bulb, and its contents are at room temperature or somewhat above, say in the neighborhood of 100 F. The expansible liquid will be at the point represented by the meniscus 2a. The unheated bar ill, or the container and bulb, are then moved relatively to bring the bar into contact with the open end of the bulb, as indicated in dotted outline in Figure 1. What may be termed an excess voltage is now impressed on the bar to heat it quickly to a temperature to cause fusion of the end of the tube in contact with it. During this rapid heating of the bar no appreciable heating of the charge in the bulb occurs as the heat transmitted by the attenuated walls of the tubulated neck is rapidly absorbed by the cooling medium. Accordingly, before any expansion of the charge takes place, the end of the tubulated portion is fused to the bar as illustrated at :ra: in Figure 2. This initial fusion of the bar and the glass tightly closes the opening in the neck.

When this initial closure of the tubulated end occurs, the voltage on the bar is then adjusted to what may be called the running voltage and at the same time valve 1 is opened to admit relatively cold liquid, say in the neighborhood of 0 F. to the container 4. This flows upward around the bulb and overflows into the trough 8, as shown in Figure 3. The body of the bulb and the charge therein are rapidly reduced in temperature thus causing the charge to contract. This tends to create a vacuum in the bulb since, as above stated, the end of the tubulated neck is closed. While this cooling of the charge is taking place, the heat supplied bythe bar is effecting the fusing of the greater portion of the bulb neck which extends above the cooling medium. The glass becomes plastic and flows together as a homogeneous mass as indicated at y in Figure 3. Since there is no positive pressure in the bulb due to the cooling of its contents, indeed since there is in all likelihood a negative pressure in the bulb, the molten material is drawn together so that the sealing of the tubulated end proceeds to a good depth.

When the sealing has been thus accomplished, the bar and bulb are slowly separated, as seen in Figure 4, the voltage being left on the bar so that the neck of the sealed bulb may beproperly annealed according to the method disclosed in Letters Patent No. 2,031,660 granted to me on February 25, 1936. As there explained, the separation of the bar and bulb is controlled at such a slow rate that a long thread is not formed between the minute portion of the glass adhering to the bar and the end of the bulb. The glass readily separates leaving a deeply sealed end lb on the bulb as seen in Figure 4.

When the scaling is thus completed and the bulb has separated entirely from the bar the flow of cooling liquid is shut off by closing the valve 1. The overflow of this liquid cases, leaving the container filled with the surface of the liquid near the slowly moving heated bar. During the further separation of the bar from the bulb, while the annealing is being accomplished, the cooling liquid is heated so as to be ready for the next bulb to be sealed.

1 claim:

1. The method of sealing a bulb of frangible material having a body and an open tubulated portion in close proximity thereto and containing a charge, comprising an expansible liquid, capable of completely shattering the bulb when it is sealed and heated to a predetermined temperature; which method comprises maintaining the body and its charge at substantially room temperature to prevent expansion of the liquid while heating the end of the tubulated portion to a fusing temperature to close it initially, reducing the temperature of said body and charge to below their temperature at the time of said initial closure and continuing the heating of the tubulated portion at fusing temperature thereby effecting a deep sealing thereof.

2. The method of sealing a bulb of frangible material having a body and an open tubulated portion in close proximity thereto and containing a charge, comprising an expansible liquid, capable of completely shattering the bulb when it is sealed and heated to a predetermined temperature; which method comprises maintaining the body and its charge at substantially room temperature to prevent expansion of the liquid while rapidly heating the end of the tubulated portion to a high fusing temperature to close it initially, reducing the temperature of said body and charge to below their temperature at the time of said initial closure and continuing the heating of the tubulated portion at a lower fusing temperature than that at the time of said initial closure thereby effecting a deep sealing thereof.

3. The method of sealing a bulb of frangible material having a body and an open tubulated portion in close proximity thereto and containing a charge, comprising an expansible liquid, capable of completely shattering the bulb when it is sealed and heated to a predetermined temperature; which method comprises maintaining the body and its charge at a temperature in the neighborhood of 100 F. to prevent expansion of the liquid while heating the end of the tubulated portion to a fusing temperature to close it initially, reducing the temperature of said body and charge to below their temperature at the time of said initial closure and continuing the heating of the tubulated portion at fusing temperature thereby effecting a deep sealing therefor.

4. The method of sealing a bulb of frangible material having a body and an open tubulated portion in close proximity thereto and containing a charge, comprising an expansible liquid, capable of completely shattering the bulb when it is sealed and heated to a predetermined temperature; which method comprises maintaining the body and its charge at a temperature below said predetermined temperature to prevent expansion of the liquid while heating the end of the tubulated portion to a fusing temperature to close it initially,

reducing the temperature of said body and charge to below their temperature at the time of said initial closure and continuing the heating of the tubulated portion at fusing temperature thereby effecting a deep sealing thereof.

5. The method of sealing a bulb of frangible material having a body and an open tubulated portion in close proximity thereto and containing a charge, comprising an expansible vliquid, capable of completely shattering the bulb when it is sealed and heated to a predetermined temperature; which method comprises maintaining the body and itscharge at a temperature below said predetermined temperature to prevent expansion'of said liquid while the end of the tubulated portion is initially closed by fusing it to a hot solid at fusing temperature, followed by reducing the temperature of said body and charge to below their temperature at the time of said initial closure while maintaining the tubulated portion at fusing temperature by prolonged contact with said hot solid, thereby effecting a deep sealing of the tubulated portion.

6. The method of sealing a bulb of frangible material having a body and an open tubulated portion in close proximity thereto and containing a charge, comprising an expansible liquid, capable of completely shattering the bulb when it is sealed and heated to a predetermined temperature; which method comprises initial-1y sealing lightly the end of said tubulated portion by rapidly fusing it by contact with a solid heated to fusing temperature, while maintaining the body and its charge at a temperature below the said predetermined temperature; followed by continuing the contact of the lightly sealed end of the tubulated portion with the said heated solid while reducing the temperature of said body and charge to below their temperature at the time of said initial light sealing, thereby effecting a deep sealing of said tubulated portion.

ALBERT J. LOEPSINGER. 

